A system consisting of a composite tube between two end fittings forms a lightweight transmission shaft which may be used to efficiently transmit static and dynamic torsional and longitudinal stresses in power transmission applications. Such systems are required to have good torsional, static and fatigue strength coupled with a high whirling resistance. To achieve the latter, low shaft densities, large diameters, reduced length and high longitudinal modulus are all advantageous characteristics. However, for any specific design application the lengths and diameters of the shafts are often fixed between narrow limits. A material combination with high specific axial modulus (high longitudinal modulus and low density) is required to produce a shaft with high resistance to whirling. To achieve this, composite tubes reinforced with high modulus fibres and in particular carbon fibre reinforced plastics (CFRP) are the materials of choice.
Fiber reinforced composite shafts exhibit advantages over metallic shafts, i.e., they are lighter in weight, more resistant to corrosion, stronger, and more inert. Fibre reinforced drive shafts comprising both glass fibers and carbon fibers in a resinous matrix have been disclosed by Union Carbide Inc in U.S. Pat. No. 4,089,190, issued in 1978.
Tubular fibre reinforced composites have been proposed, as demonstrated by Reinhold Engineering in U.S. Pat. No. 2,882,072 issued in 1959, by Koch Ind. Inc U.S. Pat. No. 3,661,670 issued in 1972, and by British Aircraft Corp. Ltd in GB1356393 issued in 1974. Vehicle drive shafts from tubular fibre reinforced composites, as demonstrated by Union Carbide in U.S. Pat. No. 4,041,599 issued in 1977, and by Celanese Corporation in U.S. Pat. No. 4,171,626 issued in 1979. Here the filaments bearing an uncured thermosetting resin are wound around a mandrel until the desired thickness has been established, whereupon the resinous material is cured. Zones or layers are positioned circumferentially within the wall of the shaft in the specific angular relationships there disclosed. The transmission of torque into the composite shaft through mechanical and adhesive joints is the subject of a series of further Celanese US patents granted in 1980-1981: U.S. Pat. Nos. 4,185,472, 4,187,135, 4,214,932, 4,236,386, 4,238,539, 4,238,540, 4,259,382 and 4,265,951. Mechanical fixing of a tubular composite shaft through an internally fitted tubular metallic splined interface is described in Mitsubishi Motors Corp. patent JP2001065538. GKN patent 2026651, 1979, claims an adhesively bonded torsion joint bonded to each ply layer through a stepped or conically machined composite wall to a matching end fitting. Loehr and Bromkamp patent GB2207732, 1989, claims a torsional joint formed by the frictional connection between a composite tube containing a wedge shaped layer with high helix angle and an internal cylindrical metallic spigot where the external spigot diameter is >0.2 mm greater then the internal diameter of the composite. Volkswagen patent DE3936999 issued in 1990, claims a joint made to the outside of a thickened shaft end and a knurled metallic end fitting. Daimler Benz patent GB2071812 issued in 1981, claims a connecting element with peripheral teeth pressed onto a fibre reinforced plastic tube in such a way that the connecting element effects a positively locked rotationally fast junction. Hitachi patent US2003/207715, 2003, uses a self aligning metallic spigot with external serrated teeth which pushes into the internal diameter of a composite tube containing an inner circumferential layer of reinforcement in the joint area.
US patent application US 2006/0258469, assigned to the present applicant and incorporated herein by reference, recites a design and method of producing a composite shaft with cylindrical end portions wherein all helical plies of fibre layers are exposed on the outer surface over which a metallic end coupling is attached through a push fit splined interface. The joint may be strengthened by internally reinforcing the main shaft with an interference fit tubular plug.